1. Field of the Art
This invention relates to a device for detecting three-dimensional (3D) shapes and conditions of an elongated flexible body, for example, 3D shapes and conditions of bends in an endoscopic flexible insertion tube which has been introduced into a body cavity of a patient.
2. Prior Art
For instance, in the case of an endoscope for examination of lower digestive ducts, its insertion tube needs to be inserted into through a complicate path of insertion which contains three-dimensional bends, more specifically, through the intestinum rectum, sigmoid colon, and lower, transverse and ascending colons. Besides, the path of insertion is not always maintained in stable conditions and can easily change into different conditions upon application of an external force. Therefore, as the insertion tube is inserted along a path of insertion, in some cases the fore leading end of the insertion tube is pushed against an intracavitary wall portion and stuck on that intracavitary wall portion failing to advance to farther target points. In this manner, great difficulties are often experienced in operating the insertion tube of an endoscope along a path of insertion, and the insertion of the endoscopic insertion tube can impose an extremely great burden on the part of the patient unless it is operated with meticulous skill.
In consideration of the foregoing situations, various attempts have thus far been made to the development of a device which can three-dimensionally grip the shape of an endoscopic flexible insertion tube which has been introduced into a body cavity. It has been known, for example, from Japanese Laid-Open Patent Application H5-91972, to employ a pair of fiber optics having obliquely cut end faces connected at a predetermined open angle relative to each other, detecting conditions of a bend in the insertion tube by calculating the open angle between the end faces of the two fiber optics.
Further, it has been known, for example, from Japanese Laid-Open Patent Application 2002-131009, to detect a three-dimensional shape of an endoscopic biopsy channel by the use of four sense coils each consisting of four single-core coils and capable of detecting a magnetic field in the same direction and on the same straight line. The four sense coils are located at four equidistant spatial positions on an orbit around a bed on which a patient lies, while, for example, 16 source coils which are adapted to produce different high frequency drive signals are provided on a probe to be introduced into a body cavity of the patient through a biopsy channel within an insertion tube of an endoscope. In this case, coordinates of spatial positions of the respective source coils are calculated on the basis of magnetic field data of the source coils to detect the three-dimensional shape of the endoscopic biopsy channel in which the probe has been inserted, that is to say, to detect the three-dimensional shape of the insertion tube of the endoscope.
In this connection, in a case where spliced fiber optics couples are used in the manner as in the firstly mentioned prior art Japanese Laid-Open Patent Application H5-91972, four fiber optics couples are required to detect the shape of a bent portion at a certain position of an endoscopic insertion tube, necessitating to locate four fiber optics couples at intervals along the length of the endoscopic insertion tube. Therefore, in order to enhance resolution over the distance in the longitudinal direction of the insertion tube, namely, in order to increase the detection points along the length of the insertion tube, it becomes necessary to provide an extremely large number of fiber optics couples at short intervals along the length of the endoscopic insertion tube. On the other hand, in the case of secondly mentioned prior art Japanese Laid-Open Patent Application 2002-131009, it is an essential requisite to provide a bed with sense coils for detection of a 3D shape of the endoscopic insertion tube, which requires to make adjustments of a patient's lying position relative to the sense coils in addition to complicate signal processing operations.